Various food storage techniques have been developed to provide otherwise perishable food products, and particularly vegetables. Many of these techniques involve thermal treatments to destroy microorganisms. However, thermal treatments are also known to adversely affect certain organoleptic properties, and especially the texture of vegetables.
Studies have been conducted for treatment of vegetables to improve firmness of the vegetables. One approach has been the use of “low-temperature, long-time” treatments or ‘blanching’ with and without calcium treatment of carrots and other vegetables for batch production. Some work focused on a calcium or low temperature treatment that occurs in the can for canned vegetables, although some work used a batch blanch prior to canning.
U.S. Pat. No. 5,607,712 to Bourne describes a method of improving firmness in frozen vegetables by a two-step blanch prior to freezing consisting essentially of a lower temperature blanch to activate pectin methyl esterase in the vegetable to increase firmness followed by a higher temperature blanch to inactivate enzymes thereby to prevent the development of off flavors during frozen storage is retained when the frozen vegetables are canned and heat sterilized. This patent asserts that the firming effect is accentuated when the food grade calcium salt is added or when a food grade acid is added to reduce the pH below 4.5. The greatest firming effect is stated to be obtained when both a food grade acid and a food grade calcium salt are added. See the Abstract.
U.S. Pat. No. RE 40,232 to Zittel describes a method and rotary blancher for processing food product using a heat transfer medium and directed flows of a fluid that can comprise a liquid, a gas, a vapor or a combination thereof The blancher and method are described to be used to process food product by blanching, cooking and pasteurizing, and is stated to be suited for processing relatively heavy food products having a density of at least 55 lbs/ft.sup.3 using discharged liquid and gas, and also to be suited for processing food products having a lesser density using only discharged gas. See the Abstract.